The invention relates generally to animal feed nutrition and, more specifically, to feeds containing vegetable meals with a combination of proteases to improve the digestibility of protein and amino acid.
As early as 1940s, animal feedstuff such as meat and bone meal and fishmeal were favored as protein sources. The onset of World War II caused an increased demand for meat products but the supply of imported meat proteins was limited. With increased knowledge on food safety, there are increasing public concerns about the health and safety of animals fed rendered meat byproducts, coupled with excessive phosphorous in poultry excreta. By 1998, cereal grains such as oilseeds and legumes already provided 30-60% of dietary amino acids. It is estimated that more than 98 percent of plant protein used in poultry feeds is from soybean meal, providing more than 66 percent of all the protein in poultry diets. The high demand for soybean meals is reflected in the estimated production of 216.9 million metric tons in 2004 with United States as the largest producer. Broilers and turkeys consume about 44 percent of all the soybeans used for livestock in the United States, with layers consuming an additional 7 percent, for a total of 51 percent. The high demand for soybean meal, as well as other plant protein sources, is in part driven by the ban of meat and bone meal in animal feeds in many developed countries to reduce the risk of BSE. Soybean meal is now widely used as the primary source of crude protein in poultry and swine diets due to its higher content of essential amino acids such as lysine (Table 1). In poultry feeds, soybean meals are added to provide crude protein at 23, 20 and 18% in starter, grower feeds and finisher diets according to the recommendation of the National Research Council (1994).
Although the crude protein content in soybean meals ranges between 44-48%, not all the protein is digestible by the digestive systems of poultry and swine. This is highlighted by recent studies which show that broilers and swine excrete nitrogen at 22 and 40% respectively of their body weights per annum (Rotz, C. A. 2004. Management to reduce nitrogen losses in animal production. J. Anim. Sci. 82 (E. Suppl.):E119-E137). Much emphasis has been placed on improving farm management to increase the nitrogen retention in animals (Ferket, P. R., E. van Heugten, T. A. T. G. van Kempen, and R. Angel. 2002. Nutritional strategies to reduce environmental emissions from nonruminants. J. Anim. Sci. 80 (E. Suppl. 2): E168-E182). In addition, the quality of crude protein significantly affects the amino acid digestibility, which was observed by Dilger et. al. (Dilger. R. N., Sands. J. S., Ragland. D., Adeola. O. 2004. Digestibility of nitrogen and amino acids in soybean meal with added soyhulls. American society of animal science. 82: 715-724) when soy hulls were added to diets containing soybean meal as the sole source of amino acids. It is therefore a common practice for feed mills to add exogenous proteases and synthetic amino acids, such as methionine, threonine, and lysine to increase and balance the amino acids in the animal diets (Chung C., Pettigrew J. E. 1998. Economics of soybean biotechnology in the livestock industry. International food and agribusiness management review. JAI Press Inc. 1(3): 373-385). The use of exogenous protease to increase bioavailability of amino acids has been demonstrated in in vitro study (Caine. W. R., Verstegen. M. W. A., Sauer. W. C., Tamming a. S., Schulze. H. 1998. Effect of protease treatment of soybean meal on content of total soluble matter and crude protein and level of soybean trypsin inhibitors. Animal feed science technology. 71: 177-183) and in swine (Caine. W. R., Tamming a. S., Sauer. W. C., Verstegen. M. W. A., Schulze. H. 1999. Bacterial contributions to total and endogenous recoveries of nitrogen and amino acids in ileal digesta of newly weaned piglets fed protease-treated soybean meal. Livestock production science. 57:147-157). Judging form the number of publications on feed enzymes, it is obvious that much emphasis has been placed on enzymes for non-starch polysaccharides (xylanase, cellulase), and phytates (phytase). Very little is known of the effect of exogenous protease on nitrogen metabolism in poultry and swine.
The high crude protein content in soybean meal makes it an ideal primary source of protein in poultry and swine feeds. The shift from animal to vegetable proteins in the wake of Bovine Spongiform Encephalopathy (BSE) in Europe has increased the global demand for soybean meal tremendously over the last few years. Recent studies have shown that despite the presence of various endogenous proteases in the digestive systems of poultry and swine, significant amount of nitrogen is still excreted by these animals into the environment (Rotz, 2004; Ferket et al., 2002). The inefficient utilization of nitrogen in these animals will result in both pollution and economic loss to the livestock operators. Many commercial feed enzymes use a single source of protease for the improvement of protein utilization in corn-soybean diets. Our results show that the amount of amino acid hydrolyzed by a single neutral protease is very limited, and will therefore not significantly and improve the bioavailability of nitrogen in corn-soybean diets.